Internal combustion engines include intake and exhaust valves that can be actuated by cam lobes of at least one camshaft. In some configurations the camshafts are constructed with sliding camshaft assemblies having multiple steps for varying the lift distance of an engine valve. For example, a two-step sliding camshaft may include a high lift cam lobe position for lifting an engine valve to a maximum distance, and a low lift cam lobe position for lifting the engine valve below the maximum lift distance.
At least one sliding camshaft actuator is fixed on an internal combustion engine for changing position between the multiple cam lobes. Particularly, at least one actuator pin of a camshaft actuator is operative to selectively engage displacement grooves configured on the periphery of camshaft barrels formed on the sliding camshaft assembly. As the camshaft assembly rotates, an actuator pin is selected to move into a displacement groove of the camshaft barrel which causes the sliding camshaft assembly to shift into a different position along the camshaft axis. When a sliding camshaft shifts position, the intake and/or exhaust valves are actuated differently in accordance with the changed cam lobe position, e.g., a sliding camshaft may move from a high lift cam lobe position to a low lift cam lobe position, which in turn will cause the engine operation to be different.
Thus, the sliding camshaft actuator is an important component in the proper operation of a VVL sliding camshaft system, particularly the actuator's pin position relative to extending into, and retracting from, the displacement grooves into the camshaft barrels. The actuator's pin position is tracked by a sensing device which outputs a digital signal indicative of the pin position, e.g., a signal output transition from LOW to HIGH is indicative of an extended pin position, and a signal transition from HIGH to LOW is indicative of a retracted pin position. Monitoring the pin position sensor output signal allows the engine controller to determine if the camshaft actuator is responding properly to its commands to actuate the pin(s) for changing variable valve lift status.
It is appreciated that output signals from sensing devices are susceptible to electrical noise generated by the outside environment or other components during vehicle operation. Such electrical noise could be read and falsely perceived by the engine controller as a pin position state change which, in turn, could lead to a diagnostic fault code being set and remedial action being inadvertently performed. Thus, there is a need for a reliable means of noise filtering a sliding camshaft actuator pin position output signal to prevent false feedback to the engine controller.